2. The main aim of seed production is to produce genetically
pure and good quality seed.
Variety: Is a group of plants having clear distinguished
characters which when reproduced either sexually or asexually
retains these characters
3. Developmental Variation
Minor Genetic Variation
Selective influence of Diseases
Techniques of the Breeder
Breakdown of male sterility
Improper / defective seed
Factors responsible for loss of genetic purity
(kadam ., 1942)
4. • Seed crop is grown in difficult environmental conditions.
• For several consecutive generations the developmental
variations may arise as differential growth response.
To avoid or minimize such developmental variations the
variety should always be grown in adaptable area
1. Developmental Variation
5. a. Contamination through field – self sown seed or volunteer
b. Seed drill – if same seed drill is used for sowing 2 or 3 varieties
c. Carrying 2 different varieties adjacent to each other.
d. Growing 2 different varieties adjacent to each other.
e. Threshing floor
f. Combine or threshers
g. Bags or seed bins
h. During seed processing
It would be necessary to rogue the seed fields at different
stages of crop growth
2. Mechanical mixtures
6. • It is not of much importance as the occurrence of
spontaneous mutations is very low i.e. 10-7.
• If any visible mutations are observed they should be
removed by rouging.
7. • It is an important source of contamination in sexually
propagated crops due to introgression of genes from unrelated
• The extent of contamination depends upon the amount
of natural cross-fertilization
• Natural crossing is main source of contamination in cross-
fertilized or often cross-fertilized crops.
• The extent of genetic contamination depends on breeding
system of the species, isolation distance, varietal mass and
To overcome the problem of natural crossing isolation
distance has to be maintained.
4. NATURAL CROSSING
8. When seed is multiplied in large areas only small
quantities of seed is taken and preserved for the next years
Because of such sub-sampling all the genotypes will
not be represented in the next generation and leads to change
in genetic composition. This is called as genetic drift.
5. Genetic drift
9. Some minor genetic changes may occur during production
cycles due to difference in environment.
Due to these changes the yield may be affected.
To avoid such minor genetic variations periodic testing of the
varieties must be done from breeder’s seed and nucleus seed in
Minor genetic variation is a common feature in often cross-
pollinated species; therefore care should be taken during
maintenance of nucleus and breeder seed.
6. Minor genetic variation
10. • In case of foliar diseases the size of the seed gets affected due
to poor supply of carbohydrates from infected photosynthetic tissue.
• In case of seed and soil borne diseases like downy mildew and ergot of
Jowar, smut of bajra and bunt of wheat, it is dangerous to use seeds for
commercial purpose once the crop gets infected.
• New crop varieties may often become susceptible to new races of
diseases and that leads to these varieties may become out of seed
(Proper plant protection - major pests and diseases)
7. Selective influence of diseases
11. • Instability may occur in a variety due to genetic
irregularities if it is not properly assessed at the time of
• Premature release of a variety, which has been breed for
particular disease, leads to the production of resistant and
susceptible plants which may be an important cause of
– When sonalika and kalyan sona wheat varieties were
released in India for commercial cultivation the genetic
variability in both the varieties was
still in flowing stage and several secondary
selections were made by the breeders.
8. Techniques of breeder
12. 9. Breakdown of male sterility
10. Improper seed certification
Generally in hybrid seed production if there is any
breakdown of male sterility in may lead to a mixture of F1
It is not a factor that deteriorates the crops varieties, but if
there is any lacuna in any of the above factors and if it has
not been checked it may lead to deterioration of crop
13. Horne (1953) had suggested the following methods for
maintenance of genetic purity;
1. Use of approved seed in seed multiplication
2. Inspection of seed fields prior to planting
3. Field inspection and approval of the Crop at critical stages
for verification of genetic purity, detection of mixtures,
weeds and seed borne diseases.
4. Sampling and sealing of cleaned lots
5. Growing of samples with authentic stocks or Grow-out test
Maintainance of genetic purity during seed production
14. 1. Providing isolation to prevent cross fertilization or
2. Rouging of seed fields prior to planting
3. Periodic testing of varieties for genetic purity
4. Grow in adapted areas only to avoid genetic shifts in the
5. Certification of seed crops to maintain genetic purity and
6. Adopting generation system
Steps suggested by Hartman and Kester (1968) for
maintaining genetic purity
15. 1. Control of seed source
2. Preceding crop requirement
4. Rouging of seed fields
5. Seed certification
6. Grow out test
Safe guards for maintenance of genetic purity
16. Appropriate class from the approved source for raising a
There are four classes of seed, which are given and
defined by Association of Official Seed Certification agency
– Nucleus Seed
– Breeder Seed
– Foundation Seed
– Certified seed
1. Control of Seed Source
18. This has been fixed to avoid contamination
through volunteer plants and also the soil borne diseases.
2. Preceding Crop requirement
3. Rouging of Seed Fields:
• The existence of off type plants is another source of
• Off type plants differing in their characteristics
from that of the seed crop are called as off types.
• Removal of off types is referred to as roughing
19. a. Segregation of plants for certain characters or mutations
b. Volunteer plants from previous crops or
c. Accidentally planted seeds of other variety
d. Diseased plants
Off type plants should be rouged out from the seed plots
before they shed pollen and pollination occurs. To
accomplish this regular supervision of trained personnel is
The main sources of off types
• Isolation is required to avoid natural crossing
with other undesirable types, off types in the fields and
mechanical mixtures at the time of sowing, threshing,
processing and contamination due to seed borne diseases
from nearby fields.
• Protection from these sources of contamination is
necessary for maintaining genetic purity and good quality
21. • The main objective of seed certification is to make available
seeds of good quality to farmers.
• To achieve this qualified and trained personnel from SCA
carry out field inspections at appropriate stages of crop
• They also make seed inspection by drawing samples from
seed lots after processing.
• The SCA verifies for both filed and seed standards and the
seed lot must confirm to get approval as certified seed.
5. Seed Certification
22. Varieties that are grown for seed production should be
periodically tested for genetic purity by conducting GOT to
make sure that they are being maintained in true form.
GOT test is compulsory for hybrids produced by manual
emasculation and pollination and for testing the purity of
parental lines used in hybrid seed production.
6. Grow-out test
23. It is the number of seeds to be produced from a single seed when it is
sown and harvested.
At the time of release of a variety, small quantity of seed normally known
as nucleus seed is available with the plant breeder. Commercial quantity of
seed is produced after a series of multiplication steps. Multiplication and
distribution of high quality seed of improved varieties is a crucial step in the
Seed Multiplication Ratio
25. SRR is the percentage of area sown out of the total area of crop
planted in the season by using certified/quality seeds other than
the farm saved seed. So, it is a measure of cropped area
covered with quality seed.
According to National Seed Policy-2002, in order to achieve
the food production targets of the future, a major effort will be
required to enhance the seed replacement rates of various
Seed Replacement Rate or Seed
Replacement Ratio (SRR)
26. What SRR denotes?
• A better seed replacement rate shows a better
utilization of the Certified/Quality Seeds.
• Certified seeds are better in productivity, hence the SRR
is directly proportional to productivity.
• Thus, higher the Seed Replacement Ratio, higher is
production as well as productivity.